Bed Bugs Aren’t Just a Problem in Paris. Here’s Why

The news reports are alarming to say the least. Paris, the city known for its style, cuisine, and amour, has a bed bug problem. Video of the insects crawling over Metro seats, in hotels, and swarming buses and movie theaters swept the internet, and bed bug anxiety reached a new high.

But what’s behind the Parisian invasion? How did bed bugs launch such a widespread infestation of the city? With Paris hosting the first Olympics in the post-COVID-19 era next summer, those questions aren’t just matters for idle conversation.

The reality is that the infestation didn’t happen overnight. It’s likely that Paris, as well as other cities and even less-densely populated areas around the world, harbor a consistent, and persistent bed bug problem. And with the boom in travel since the pandemic, people in Paris are noticing them.

A number of factors keep bed bugs surviving and thriving, say entomologists, many of which are directly related to human behavior. Part of the problem may be the way we manage the pests. Unlike mosquitos and ticks, which government groups address with wide-scale, community-wide spraying and eradication efforts, bed bugs are seen more as an individual, rather than a societal, problem. And not everyone has the time or money to take the proper steps to get rid of them, so the insects continue feeding, breeding, and spreading to find new hosts.

Contrary to anecdotal reports, bed bugs aren’t the result of poor hygiene and aren’t limited to lower income communities. It’s just that less advantaged people don’t have the resources to eradicate them. “I’ve dealt with reports from five star hotels, first class airline seats, and high end apartments,” says Zachary DeVries, assistant professor of entomology at the University of Kentucky. “Anybody can get bed bugs, but only those with resources can get rid of them.”

More From TIME

That’s why, particularly in densely populated cities like Paris, there may be reservoirs of bed bug populations in more disadvantaged communities, which then spread as the insects hitch rides on public transportation, into restaurants, movie theaters, retail stores—essentially anywhere people go.

But there are other reasons why the bugs  are so difficult to eradicate.

Humans and bed bugs—a long, and close, history

Bed bugs are unique in that they depend almost exclusively on humans to survive. They only need blood—while they feed on livestock and chicken blood they preferentially suck on people—to keep them going. If they have a human host, they don’t even need water. And they established this parasitic relationship centuries ago. Cave drawings depict bed bugs, while wood prints captured their flat, tiny bodies and when cameras were developed, the first pictures of them emerged in the 1800s.

Culturally, bed bugs have also shaped human history. Some historians suggest that the annual practice of spring cleaning may have begun as an attempt to flush out bed bugs, which tend to be less active during the colder winter months, before they were reinvigorated in the spring and summer.

“They are reclusive and extremely shy,” says Gail Ridge, an associate scientist at The Connecticut Agricultural Experiment Station, a state and federally funded research facility. “They are dependent on human beings to live, so they live a conflicted life of terror, since we are the prime predator on the planet. So they can only survive by having a series of mechanisms to elude our efforts to kill them.”

One of them may be a remarkable ability to inbreed. For most living things, finding new, and distantly related, mates is key to passing on genes and keeping their kind going. Inbreeding is normally a species-killer, since mating with genetically related members can introduce dangerous, and potentially lethal, mutations. But bed bugs aren’t saddled with such limitations; in fact, a single female carrying eggs can seed a new colony of bugs in a location as the future generations breed among themselves. “We have seen brother-sister matings for 20 to 30 generations and nothing happens,” says DeVries. “The later generations are just as happy and healthy as the first.”

How pesticides solved the bed bug problem—before making it worse

The most aggressive human efforts to eradicate the bugs  involve pesticides such as DDT and organophosphates. They were so effective that from the 1950s to the 2000s, these chemicals largely eliminated bed bugs from the developed world. But bans on them after their toxic effects on human health were discovered gave the bugs a break, along with broader international trade rules that opened the exchange of goods across the world. “Bed bugs became a problem after we went through the ban on organophosphates indoors,” says Jody Gangloff-Kaufmann, an entomologist at the New York State Integrated Pest Management program at Cornell University. The bugs came back in the early 2000s, spread primarily along trade routes from developing nations to industrialized countries, and flourished in a new world with less aggressive chemical attacks. In 2010, cities like New York experienced massive bed bug infestations, with alarming sightings closing retail stores in Soho and South Street Seaport. Even workplaces weren’t immune, as the insects infiltrated Time Warner’s headquarters near Central Park as well.

Worse, the new generations of bugs were highly resistant to any chemicals used to treat them. “The bugs we have today are not the same as their grandparents,” says Dini Miller, professor of entomology and urban pest management specialist at Virginia Tech. “We have thick-skinned, hard-drinking, mutant bed bugs.”

Exposure to the pesticides has pushed the bugs to develop harder exoskeletons, which prevents the chemicals from penetrating into their bodies for two reasons. One,, “bed bugs walk on hooked claws and lift their bodies off the ground,” says Nina Jenkins, an affiliate professor of entomology at Penn State University. “So the amount of bed bug that contacts a surface when they are walking is a very small proportion of their body—so if they walk over a toxin-treated surface, they don’t absorb enough to kill them.”

And even if the bugs do absorb some of the chemicals, they have developed enzymes that can break apart toxins and neutralize them. “We may knock them down and they look dead, but four hours later, they get up and shake it off because the enzymes in their bodies are breaking down the insecticide and they can recover,” says Miller. “We have basically killed off all the bugs that are susceptible to insecticides, and selected for the resistant ones. We’ve done it to ourselves.”

Not only have people introduced pesticides that have generated new super breeds of resistant bugs, but humans have also removed one of the bed bug’s primary predators: cockroaches. “Cockroaches, like bed bugs, can get into cracks and crevices and they hunt bed bug eggs,” says Ridge. “But now that cockroaches are being knocked out in many cities, bed bugs have no predator.”

Read more: Why Bed Bugs Are Becoming So Much Harder to Kill

They never went away

These resistant bugs are getting hardier and hardier. Cross breeding with different populations makes them even more fertile, says Ridge. She has crossed two different lab populations of bed bugs and found that the fecundity of the females doubled. “I can only assume that’s happening in the wild as well,” she says, especially since bugs from different parts of the world are likely mixing and matching thanks to widespread human travel.

And thanks to the fact that simply spraying with a can of insecticide doesn’t get rid of them, these bugs are finding hospitable habitats in certain populations. “One of the things I’m seeing is a huge increase in the demographic of elderly disabled living with thousands upon thousands [of bed bugs] in their home,” says Miller. “These are individuals with 17 other problems, including physical, mental ,and financial [problems], and bed bugs are just one of them. Those are the sources that we are now seeing.”

Because the bugs aren’t being eliminated from these populations, they may continue to hitch rides to other locations where they find new hosts. “Bed bugs settle in with people who can’t deal with them effectively,” she says. So despite media reports about infestations in hotels, they are rarely the source of widespread problems, since hotels can afford effective, and often expensive, pest control measures. Individual home owners, and owners of apartment buildings, halfway houses, and nursing homes, however, often cannot.

The best ways to get rid of bed bugs

There is no single approach that effectively controls bed bugs. It takes a series of painstaking steps, performed correctly—usually with professional training—to truly get an infestation under control. “There is very little the homeowner can do to get rid of the problem,” says DeVries. Sprays that claim to eliminate bed bugs won’t truly get the job done since the bugs are resistant to most of them, and, if they are effective, they only push the bugs from one place to another. And online advice about using heat or steam by directing hair dryers or steam irons at mattresses is wrong—doing so also just drives the bugs from one place to another. Even some professional pest control services that perform heat or steam methods aren’t all effective, since they may not achieve high enough temperatures—bed bugs only die at around 125°F—or may not run the devices long enough. “I’ve heard of multi-family apartment complexes where they start at the top and work their way down, and by the time they get to the first floor, there are already reports of problems back on the top floor,” says DeVries.

As contrary as it seems, one of the most effective strategies is to not disturb the bugs as much as possible. Bed bugs don’t like to stray far from their blood meal, which means they remain in areas where people sleep and sit—hidden in cracks and crevices in mattresses and sofas. “They won’t be in the bathroom where they have to walk half a mile to feed,” says DeVries. “If you don’t disturb them, you can keep the problem concentrated to a sofa, chair or bed.” After determining where the bed bugs are, vacuuming them is the first step. Miller recommends attaching a long stocking to the outside of the vacuum hose to ensure no bugs can escape, and once the vacuuming is done, tying off the stocking and either soaking it in water to drown the bugs or disposing of them in a sealed container.

If bed bugs are crawling on clothing, putting the clothes in a hot dryer will desiccate them. Sealing the clothes once they come out of the dryer in a tight plastic bag and leaving them undisturbed for a few weeks ensures that no eggs and new generations of bugs remain.

Read more: Bed Bugs Are Most Drawn to This Color

There are also newer insecticides that don’t rely on the harmful chemicals of the past. One increasingly popular one that Miller and her team are testing is Aprehend, a fungus-based treatment that can only be applied by licensed pest control specialists. The treatment is a spore in a liquid form that is sprayed on affected areas; the contact with the fungus gives the bugs a dermal infection that kills them. The reason it’s so effective, says Jenkins, who co-developed the product at Penn State and founded a company to commercialize it, is that it’s designed to remain active for up to three months. Millions of fungal spores are spread in a thin band around the areas where bed bugs travel, and just a few steps on the treated area will bind those spores to their claws. They then bring those spores back to their nests, which may be in hidden areas no human treatment could ever reach, and spread them to other bugs, and ultimately any exposed bug dies of the fungal infection. “To be completely honest, it shocked us how successful this product has been,” says Jenkins.

Sealing infested articles or clothing can also dry them out, but bed bugs can live for months without feeding, so starving them out could take a while and it’s not always practical—nor is it guaranteed to work. Gangloff-Kaufmann had a colleague who put some bugs in a freezer for five years and once thawed, one survived.

Dust-based treatments such as silica dust can also be effective in killing bugs by suffocating them, but requires precise application since breathing in the dust can also be harmful to people, leading to cancer and lung disease.

“No one strategy is going to be effective but if you start stacking them up you could eventually catch everything,” says DeVries. “Vacuuming doesn’t get everything, but steaming could get the bugs that vacuuming misses. And if steaming doesn’t get them, then insecticides like Aprehend could. Then, setting up physical barriers could help too. We don’t know if one is working better than the other, but we know that if you incorporate them all, it could be an effective management plan.”

Even more important, entomologists agree, is recognizing that bed bugs aren’t just an individual’s problem. They should be treated as a societal problem with a societal solution. But that’s been challenging, since bed bugs don’t transmit diseases like mosquitos and ticks do. While they feed on human blood, they don’t pass on whatever they pick up, since they have a unique ability to fracture the DNA of pathogens they ingest so they are no longer capable of causing disease. “If you imagine the DNA of a virus like polio or HIV or influenza as a glass vase, once it is ingested by a bed bug, it shatters,” says Ridge. That makes controlling bed bugs a hard sell for government intervention, since they don’t technically cause public harm other than a general sense of anxiety and discomfort. Yet, says Gangloff-Kaufmann, “I like to call bed bugs a communicable insect.” DeVries agrees, noting that “everybody uses public transportation, everybody uses airlines, and everybody goes to the movies. Everybody ventures into society, and the bugs have constant opportunity to reinfest and reinvade everywhere. We let them persist. Ultimately unless they are dealt with on a broader, community-wide scale, the problem will not go away.”